Sureños (Spanish for "Southerners") are a group of Mexican American street gangs with origins in the oldest barrios of Southern California. There are hundreds of Sureño gangs in California, and each has its own identity on the streets. Although they are based in Southern California, their influence has spread to many parts of the US and other countries as well.

The gang's alleged roots came from a jail discussion between the Mexican Mafia (La EME) and Nuestra Familia (NF). Those who sided with La EME aligned themselves in the south (sureño = southerner) while those that sided with the NF aligned themselves in Northern California (norteños = northeners). Besides Southern California, Sureños can be found in more than 30 states (primarily in southwestern and central states. Norteños appear mostly in the northern areas of California, but are also present in numbers in western states like Washington, Oregon, Colorado, and Utah. They also have a small presence in the San Fernando Valley area of Los Angeles and in the south side of St. Louis, Missouri.

While increasing in influence and power throughout the years, the Sureños hierarchy is relatively unorganized, and has made enemies, such as the Green Light Maravillas, a smaller gang that broke off in order to resist paying taxes to the Sureños. Sureño gang members often use the number 13 as gang identification, as the letter "M" is the 13th letter of the alphabet to show their alliance with "La eMe" (Mexican Mafia). Sureños represent themselves with symbols and phrases such as "Sur 13", "Los Sureños" and "Sureño Trece". These identifications are accompanied by the color navy blue, silver, and white, numeric code of number 13 and the Roman numeral of XIII.

There are also many cliques in Sur 13 (a clique is like a crew that controls a few streets). An example of a Sur 13 clique is the S.S.C SouthSide Criminals, which controls a few streets in LA and Las Vegas.

The term “sureños” describes gangs professing allegiance to a gang set in southern California. The term was first used in the 1970s as a result of a California prison war between the Mexican Mafia (La EME) and Nuestra Familia (NF). This war resulted in a territorial division between gang members from northern California (norteños = northerners) who aligned with NF, and those from southern California (sureños = southerners) aligned with La EME.

On the streets of California, southern California street gangs are collectively referred to as Sureño gangs. Each gang has its own identity on the streets, and Sureño gangs share no common organizational structure; however, they are all subordinate to La EME. Within the prison system, members of these gangs often unite under the Sureño umbrella.

In addition to prison association, some individual Sureño gangs or gang members have migrated out of California and assimilated under the name Sureño, establishing themselves across the country. The gang members rarely maintain associations in California, but use the name to signal their alliance with other Sureño gangs. These gangs use names such as Sur 13, Los Sureños, Sureño Trece, or other variations.

These gangs routinely conduct low level drug sales and provide the California Mexican Mafia ten percent of their profits. Although Sureño gangs primarily profit from drug distribution, they will engage in almost any criminal activity that will turn a profit, including major theft and alien smuggling. Sureño gangs have also been associated with drug trafficking organizations (DTOs) and conduct enforcement activities on their behalf. The DTOs prefer to use these “soldiers” in some instances so that they do not risk the arrest of high level DTO members. Gang Identifiers: Sureño identifiers will always include the number 13 and will likely include “Sur” or “Sureño.”